The present invention relates generally to the field of gyroscopes and unbalances in rotating machinery and more specifically to improvements in the balancing of free rotor, flexure-suspended gyroscopes, such as those disclosed, for example, in the U.S. Pat. No. 3,077,785 by J. C. Stiles and No. 3,354,726 by W. J. Krupick et al, both assigned to the assignee of this invention.
Because gyroscopes persistently point in one direction unless acted upon by a resultant torque, they are widely used today in inertial guidance systems for aircraft, guided missiles, and space vehicles. Due to their simple operation and small size and weight, free rotor flexure-suspended gyroscopes are particularly useful in inertial guidance platforms where accuracy is needed but power, size and weight are at a premium. In this type of gyroscope, the inertial flywheel is mounted at its center of gravity on a flexible hinge which imparts rotation to the flywheel while providing a universal support about which the flywheel can pivot in any direction. Fixed pick-offs arranged beneath the flywheel provide pitch and roll signals indicative of the relative distance of the flywheel from a given pick-off. Because of the small size of the flywheel, the gyroscopic parameters of unbalance are highly sensitive to manufacturing inaccuracies. Generally speaking, unbalances with respect to the central mounting point of the flywheel are undesirable in that they make the flywheel sensitive to accelerations along and perpendicular to the flywheel spin axis. The gyroscope's function is to sense changes in orientation, not linear acceleration. In the past, certain types of unbalance were simpler to detect since spurious vibrations of the flywheel were transmitted through the gyroscope assembly and could induce vibrations in a transducer. However, in the flexure-suspended gyroscope, most of the smaller vibrations are damped out by the flexure hinge; that is, the vibrations fail to be transmitted through the hinge for external measurement.
Gyroscopic unbalances were corrected by removing material or adding material to selected portions of the flywheel. This was usually accomplished by drilling or adding small weights or by a combination of techniques. No matter how the unbalance was corrected, the unbalance detection and correction were always accomplished in completely different stages and with different equipment. The operator always introduced his own errors into a test and correction procedure which was largely trial-and-error and thus extremely time-consuming for fine balance.